Rechargeable electrochemical energy storage cells housed in plastic enclosures have become very common. They have PbO2-positive and Pb-negative electrodes at full state of charge, the electrodes surrounded by dilute H2SO4 electrolyte. Physical contact between the electrodes is prevented by a suitable form of porous insulation. There are approximately one billion six-cell configurations in use worldwide, predominantly for starting automobile engines. There are numerous other cell configurations based on essentially the same chemistry, that are used to power indoor and outdoor electric vehicles, telephone exchanges, home, office and industrial equipment, computers, servers, in load leveling applications as well as signaling and lighting applications, etc.
User complaints include a variety of difficulties that are commonly encountered in operation of these rechargeable energy storage cells and a useful service life that is too often unpredictable and limited. More specifically, as the energy storage cells of the type used to power vehicles age, their end-of-charge voltage falls, rate of gassing increases, temperature and water consumptions rise. The cells are subject to the cumulative erosive effect of charging current, in normal use, that progressively damages the integral metal support structures of the positive electrodes, resulting in disengagement of the PbO2 of the positive electrodes from the support structures and, consequently, progressive loss of energy storage capacity of the cells, eventually rendering the cells unfit for normal use.
Comprehensive descriptions of elements and compounds that feature in the present specification including compounds including the elements Ba, C, Cd, Cu, H, K, N, O, Pb, S, Sb, Sn are provided in “CRC Handbook of Chemistry and Physics”, Editor David R Lide, 83rd Edition, (2002-2003), Section 4, chapter 1.